The present invention relates to a novel polymer, particularly a novel electroconductive polymer and a precursor thereof.
As polymers used for forming electroconductive polymers there are known polyacetylenes, polyparaphenylenes, polythiophenes and polypyrroles. These polymers become employable as electroconductive polymers by being doped using certain kinds of compounds. However, the electroconductive polymers thus obtained are apt to change in quality, especially in electrical characteristics, in the air. Further, those polymers are poor in meltability and solubility so are extremely inferior in processability. These drawbacks are serious obstacles to their practical use. For example, as an application of such electroconductive polymers there has been proposed an application to electrodes for a secondary battery utilizing their reversible redox characteristic. In most cases, however, they are unstable physically or chemically in the electrolyte of a secondary battery. Therefore, it is impossible to expect a stable cyclability of charge and discharge which is a basic performance required for a secondary battery. Besides, electroconductive polymers are insoluble and unmeltable because their skeletons are each constituted by a rigid .pi. electron conjugated system, and this point is also a serious obstacle to their practical use.
As a solution to the above problems it is proposed in Japanese Patent Laid-Open No. 206170/1986 to use as the electrode material for a secondary battery an electroactive polymer obtained by doping a polymer which has a 4,4'-diphenylamine structure as a repeating unit, using an electron acceptor or donor.
However, such diphenylamine a polymer is an oligomer of a low polymerization degree, lacking in mechanical strength and moldability which the polymer should possess as a high polymer. For example, in case of using this polymer as the electrode material for a secondary battery, a soluble component will dissolve out with repetition of charge and discharge, so it is impossible to expect a stable cyclability.
Moreover, in order to impart mechanical strength and moldability to the above diphenylamine polymer in addition to good electrochemical characteristics, it is necessary to obtain a polymer which is higher in the degree of polymerization (a high polymer). But it is difficult to obtain a high polymer even according to any of processes commonly used for the preparation of polyaromatic or polyheteroaromatic compounds, such as Grignard coupling, oxidative coupling, Friedel-Crafts reaction and electrolytic oxidation polymerization. Even under severer reaction conditions, not only it is impossible to expect the realization of a higher molecular weight due to an induced hetero-linkage or crosslinking reaction, but also the polymer becomes incapable of dissolving and melting with loss in processability which processability is one of the advantages of high polymers. Further, the polymer becomes inactive electrically.
For overcoming the above-mentioned drawbacks of the prior art, the present inventors have already found out and proposed copolymers represented by the following general formula: ##STR2## which copolymers are soluble in such solvents as N-methylpyrrolidone, nitrobenzene and sulfuric acid, superior in moldability because of thermoplastic resins, and are improved in their electroactivity by being doped using electron accepting compounds, thus permitting a redox reaction to be carried out in good cyclability, so are expected for their application to various electronic devices and batteries.
However, the above copolymers involve the problem that when applied to battery electrodes, the charge/discharge capacity per electrode active material weight becomes small. Therefore, improvement in this point has been desired.